Error: Cannot find module 'mongodb'

It was working for me and also I have installed MongoDB but suddenly i got this.

what could be the problem help needed.

module.js:340

    throw err;

          ^

Error: Cannot find module 'mongodb'

    at Function.Module._resolveFilename (module.js:338:15)

    at Function.Module._load (module.js:280:25)

    at Module.require (module.js:364:17)

    at require (module.js:380:17)

    at Object.<anonymous> (/Users/SHREE/Downloads/MongoDB_Univeresity/week_2_crud.11a4d1f551db/node_js_driver_findandmodify/findAndModify/findAndModify/app.js:1:81)

    at Module._compile (module.js:456:26)

    at Object.Module._extensions..js (module.js:474:10)

    at Module.load (module.js:356:32)

    at Function.Module._load (module.js:312:12)

    at Function.Module.runMain (module.js:497:10)

It was working for me and also I have installed MongoDB but suddenly i got this.
what could be the problem help needed.
module.js:340

Hi,

It looks like you don't have the mongodb driver installed in your working directory.

You can install local to the current project directory with `npm install mongodb` or globally with `npm install -g mongodb`.